Connection

All models communicate via an optically isolated serial connection, at 9600 bps, 8 bits, no parity, and 1 stop bit (9600/8n1). Connecting to the devices can be done either via USB (U1173A cable) or Bluetooth (U1177A interface or U1117A interface).

Protocol

All models in this series use generally the same protocol, with only minor differences between models – and none within the same range.

The meters will respond to commands, which consist of a short ASCII string followed by either LF or CR+LF. The meter will either send no response at all, some ASCII text followed by CR+LF, or *E followed by CR+LF if the command given was invalid.

Some events (such as turning the rotary switch) will cause spontaneous transmissions of event notifiers. These consist of a * character, a single character and CR+LF.

*IDN?

Sending the command *IDN? causes the device to return a comma-separated four-field string, compatible with the identical GPIB command. The four fields are vendor name, model name, serial number and version:

*RST

Sending the command *RST causes the device to reset. The response is an asterisk followed by the current dial position, for example *1 indicates the first position.

SYST:BATT?

The command SYST:BATT? returns a value indicating the device's battery level. The value is in a different format depending on the model series:

The U123xx, U124xC, U127xx and U128xx models return a percentage value, like this:

36%

The U124xx models return a value like this:

+1.04200000E+02

SYST:BEEP

The command SYST:BEEP TONE make the multimeter emit a beep.

SYST:BLIT

The commands SYST:BLIT 1 and SYST:BLIT 0 turn the screen backlight on and off. There is no response. The backlight timer will still run and turn the backlight back off again if it is enabled.

FETC?

The FETC? command returns the current measured value, as a floating point ASCII string, as in the following examples:

+9.25000000E-03
+0.00000000E+00
-1.01140000E+00
-9.10200000E-01

The sign characters are always present, and the value is always in normalized scientific format. This applies even when in a mode that uses integer numbers, 11 would be transmitted as +1.10000000E+01. If no valid measurement is available, i.e. the display shows "OL" or "-OL", the transmitted value is either +9.90000000E+37 and -9.90000000E+37 respectively.

For models with dual display, the FETC? @2 command returns the current value from the secondary display, in the same format.

CONF:

The CONF: commands can be used to change modes and ranges on the multimeter. It is not to be confused with the CONF? query described below.

For a given rotary switch position, only those CONF: commands work that switch to modes that can be reached by pressing the range or shift buttons.

U124xx/U125xx models

Same as above for the U123xx, except for different ranges.

CONF?

The CONF? command queries the device's current measurement configuration.

U123xx models

This can be either one, two or three comma-separated fields. The number of fields depends on the first field's value, but the second field always denotes the measurement mode's range and resolution, and the third field is the current type (AC or DC). For example, this indicates AC voltage in the 600mV range:

V,0,AC

Mode

Resolution

Current

Meaning

V

y

y

Volts

0

Range 600mV, resolution 0.1mV

1

Range 6V, resolution 1mV

2

Range 60V, resolution 0.01V

3

Range 600V, resolution 0.1V

MV

y

y

Millivolts

1

Range 600mV, resolution 0.1mV

A

y

y

Ampere

0

Range 6A, resolution 1mA

1

Range 10A, resolution 0.01A

UA

y

y

Microampere

0

Range 60μA, resolution 0.01μA

1

Range 600μA, resolution 0.1μA

FREQ

y

y

AC frequency

0

Range 99.9 Hz, resolution 0.01 Hz

1

Range 999.9 Hz, resolution 0.1 Hz

2

Range 9.999 kHz, resolution 1 Hz

3

Range 99.99 kHz, resolution 10 Hz

4

Range 200 kHz, resolution 100 Hz

RES

y

n

Resistance

0

Range 600Ω, resolution 0.1Ω

1

Range 6kΩ, resolution 0.001kΩ

2

Range 60kΩ, resolution 0.01kΩ

3

Range 600kΩ, resolution 0.1kΩ

4

Range 6MΩ, resolution 0.001MΩ

5

Range 60MΩ, resolution 0.01MΩ

CAP

y

n

Capacitance

0

Range 1000nF, resolution 1nF

1

Range 10μF, resolution 0.01μF

2

Range 100μF, resolution 0.1μF

3

Range 1000μF, resolution 1μF

4

Range 10mF, resolution 0.01mF

DIOD

n

n

Diode

U124xx and U125xx models

The output consists of a quoted string with the meter's mode, followed by a space, two values, separated by a comma, denoting the current range, and the value of one count. The mode may optionally include a colon followed by a code denoting a submode relevant to that major mode.
For example, AC voltage mode with 1000mV range on a 10000-count U1241B would be given as:

"VOLT:AC +1.000000E+00,+1.000000E-04"

Mode

Meaning

VOLT

DC voltage

VOLT:AC

AC voltage

CURR

DC current

CURR:AC

AC current

FREQ

Frequency counter

DIOD

Diode check. No range values are given.

CONT

Continuity. No range values are given.

RES

Resistance

CAP

Capacitance

SCOU

Switch counter. No range values are given.

CPER:0-20mA

Current loop, 0-20mA setting

CPER:4-20mA

Current loop, 4-20mA setting

T1:K or T2:K

Temperature on T1 or T2, submode can be K or J, denoting the thermocouple type. Instead of range values, CEL or FAR is given, denoting the measurement is in degrees Celsius or Fahrenheit. The full response might thus be: "T1:K CEL".

U124xC

The output is very similar to the U124xx and U125xx models with a few differences and additions.

Mode

Meaning

VOLT

DC voltage

VOLT:AC

AC voltage

VOLT:HRAT

Harmonic Ratio

CURR

DC current

CURR:AC

AC current

FREQFREQ:AC

Frequency

DIOD

Diode check. No range values are given.

CONT

Continuity

RES

Resistance

CAP

Capacitance

CPER:0-20mA

Current loop, 0-20mA setting

CPER:4-20mA

Current loop, 4-20mA setting

TEMP

Internal temperature. No range values are given.

TEMP:K

Temperature, submode can be K or J, denoting the thermocouple type. Instead of range values, CEL or FAR is given, denoting the measurement is in degrees Celsius or Fahrenheit. The full response might thus be: "TEMP:K CEL".

Temperature, submode can be K or J, denoting the thermocouple type. Instead of range values, CEL or FAR is given, denoting the measurement is in degrees Celsius or Fahrenheit. The full response might thus be: "TEMP:K CEL".

SQU

Square wave output. No range values are given.

NCV

Vsense (Non-contact Voltage). Instead of range values, HIGH or LOW is given, denoting High sensivity or Low sensivity. The full response might thus be: "NCV HIGH".

STAT?

The STAT? command is used to query the current state of the device. The response is a quoted 21-byte string, like this:

"000000000110L00000000"

U123xx models

Byte

Value

Meaning

1

Max/min/avg mode

0

Off

1

On

2

Relative measurement. The last value returned from FETC? before this mode was enabled denotes the stored reference value.

0

Off

1

On

3

Trig hold-log

0

Off

1

On

4

Auto hold-log

0

Off

1

On

5

LED flashlight

0

Off

1

On

6

LCD backlight

0

Off

1

On

7

Smoothing

0

Off

1

On

8

Temp/aux mode. When on and rotary switch is in position 5 (capacitance), CONF? returns MV,1,DC, but the value returned from FETC? instead denotes the temperature, in the unit (F or C) according to the meter's configuration.

0

Off

1

On

9

Unknown (always 0)

10

Beep frequency

0

4.2kHz

1

3.8kHz (default)

2

3.4kHz

3

3.2kHz

4

Off

11

Auto power-off (APO)

0

Off

1

On

12

Unknown (always 0)

13

Unknown (always L)

14-15

Unknown (always 0)

16

Rotary switch position

0

V/Zlow

1

Voltage AC

2

Voltage DC

3

Resistance

4

Diode

5

Capacitance

6

Current

7

Microcurrent

17

Continuity mode. When enabled, the value returned from FETC? is either NAN (no continuity) or any real value to denote continuity.

0

Off

1

On

18

Unknown (always 0)

19

Battery low indicator

0

Battery OK

1

Battery low

20-21

Unknown (always 0)

U124xx models

Byte

Value

Meaning

1

Max/min/avg mode

0

Off

1

On

2

Relative measurement. The last value returned from FETC? before this mode was enabled denotes the stored reference value.

0

Off

1

On

3

Unknown

4

Unknown

5

Unknown

6

Current loop mode

0

0-20mA mode

1

4-20mA mode

7

Unknown (always I)

8

Hold mode.

0

Off

1

On

9

Unknown

10

Beep frequency

0

Off (no beeps)

C

300Hz

F

600Hz

1

1200Hz

2

2400Hz

11

Auto power-off (APO)

0

Off

1

On

12

LCD backlight

0

Off

1

On

13

Unknown (always L)

14

Unknown

15

Unknown

16

Rotary switch position

0

Voltage

1

Diode

2

Resistance

3

Capacitance

4

uA

5

mA

6

A

7

Temperature

17

Unknown

18

Unknown (always 1)

19

Unknown

20

Switch counter mode

0

increase count on rising flank (initially low)

1

increase count on falling flank (initially high)

21

Auto range

0

Off

1

On

U124xC models

Byte

Value

Meaning

1

Max/min/avg/maxminavg mode

0

Off

1

On

2

Relative measurement. The last value returned from FETC? before this mode was enabled denotes the stored reference value.

0

Off

1

On

3

Flashlight

0

Off

1

On

4

Probe socket connexion alert

0

Off

1

On

5

Unknown

6

Unknown

7

Smooth mode

0

Off

1

On

8

Trigger Hold

0

Off

1

On

9

0°C Temperature compensation

0

Off

1

On

10

Beep frequency

0

Off (no beeps)

1

3200 Hz

2

3268 Hz

3

3339 Hz

4

3413 Hz

5

3491 Hz

6

4572 Hz

7

3657 Hz

8

3746 Hz

9

3840 Hz

A

3938 Hz

B

4042 Hz

C

4151 Hz

D

4267 Hz

11

Auto power-off status

0

Off

1

On

12

Auto Hold

0

Off

1

On

13

Meter mode

L

Normal

C

Calibration

14

Unknown

15

Reserved

16

Rotary switch position

0

Zlow Voltage AC / DC (V)

1

Voltage AC (V) / H%

2

Voltage DC (V)

3

Resistance / continuity

4

Diode / capacitance

5

Current DC / AC (µA/mA)

6

Current DC / AC (A)

7

Temperature

17

Battery type

0

Primary

1

Secondary (rechargeable)

18

Battery low or Current percent

0

Off

1

Battery low or 4-20 mA mode

2

0-20 mA mode and not Battery low

19

Unknown

20

Unknown

21

DC filter (LPF)

0

Off

1

On

U125xx models

Byte

Value

Meaning

1

Max/min/avg mode

0

Off

1

On

2

Relative measurement. The last value returned from FETC? before this mode was enabled denotes the stored reference value.

0

Off

1

On

3

dB mode

0

Off

m

dBm

V

dBV

4

Unknown

5

Peak hold mode

0

Off

1

On

6

Current percent

0

0-20mA

1

4-20mA

7

Triggerhold I/B ?

8

Triggered hold mode.

0

Off

1

On

9

Zero temperature compensation?

10

Beep selection ?

11

Auto power-off (APO)

0

Off

1

On

12

LCD backlight

0

Off

1

On

13

Unknown (always L)

14

Unknown (always 0)

15

Unknown

16

Rotary position ?

17

Output status active/standby ?

18

Unknown

19

Battery low indicator

0

Battery OK

1

Battery low

20

Frequency counter prescaler

0

No prescaling

1

Divide by 100

21

Auto range

0

Manual range

1

Auto range

U127xx models

Byte

Value

Meaning

1

Max/min/avg/maxminavg mode

0

Off

1

On

2

Relative measurement. The last value returned from FETC? before this mode was enabled denotes the stored reference value.

0

Off

1

On

3

Unknown

4

Unknown

5

Unknown

6

Unknown

7

Unknown

8

Unknown

9

Unknown

10

Beep frequency

0

Off (no beeps)

1

3200Hz

2

3491Hz

3

3840Hz

4

4267Hz

11

Unknown

12

Unknown

13

Unknown (always L)

14

Unknown

15

Unknown

16

Rotary switch position

0

Zlow, V AC/DC

1

N/A (this is the "OFF" position)

2

Voltage AC (V) / LPF

3

Voltage AC (mV) / LPF

4

Voltage DC / AC (V)

5

Voltage DC / AC (mV)

6

Resistance / "smart resistance" / continuity

7

Diode / Auto

8

Capacitance / temperature

9

Current DC / AC (mA/A)

10

Current DC / AC (µA)

17

Unknown

18

Unknown

19

Unknown

20

LPF

0

Off

1

On

21

Unknown

U128xx models

Byte

Value

Meaning

1

Max/min/avg/maxminavg mode

0

Off

1

On

2

Relative measurement. The last value returned from FETC? before this mode was enabled denotes the stored reference value.

0

Off

1

On

3

dB function

0

Off

M

dBm

V

dBV

4

Probe socket connexion alert

0

Off

1

On

5

Peak-hold

0

Off

1

On

6

Current percent

0

Off

1

4-20 mA

2

0-20 mA

7

Pulse width and duty cycle trigger level

0

Negative

1

Positive

8

Trigger Hold

0

Off

1

On

9

0°C Temperature compensation

0

Off

1

On

10

Beep frequency

0

Off (no beeps)

1

3200 Hz

2

3268 Hz

3

3339 Hz

4

3413 Hz

5

3491 Hz

6

4572 Hz

7

3657 Hz

8

3746 Hz

9

3840 Hz

A

3938 Hz

B

4042 Hz

C

4151 Hz

D

4267 Hz

11

Auto power-off status

0

Off

1

On

12

Auto Hold

0

Off

1

On

13

Meter mode

L

Normal

C

Calibration

14

Voltage alert

0

Off

1

On

15

Reserved

16

Rotary switch position

0

Voltage AC (V) / LPF

1

Voltage AC (mV) / LPF

2

Voltage DC / AC (V)

3

Voltage DC / AC (mV)

4

Resistance / continuity / conductance

5

Diode / frequency counter

6

Capacitance / temperature

7

Current DC / AC (µA/mA)

8

Current DC / AC (A)

9

Square wave output

17

Battery type

0

Primary

1

Secondary (rechargeable)

18

Battery low

0

Off

1

On

19

Resolution

0

5 digits

1

4 digits

20

LPF

0

Off

1

On

21

DC filter

0

Off

1

On

LOG:

Different commands can be used to retrieve the content of the different log memories from the multimeter. Those commands allow to retrieve log entries one by one, specifying the index of the entry to retrieve each time. When the index is greater than the index of the last logged value, the multimeter will return an error (*E). The actual commands depends on the model.

The response is presented as a quoted string whose length depends on the model.

Note that each log entry is also emitted by the multimeter whenever a new value is captured to the log.

U123xx models

The valid commands to retrieve log entries are yet to be determined.

Log entries are 15 characters long. Here is an example of log entry:

"050000210000200"

Note that the position of the decimal point is not explicitly given, it must be discerned from the range.

Byte

Value

Meaning

1

Unknown (always 0)

2

Function

0

AUX

1

Voltage

2

Microcurrent

4

Current

5

Resistance or continuity

6

Diode

8

Capacitance

9

Frequency

3

Unknown (always 0)

4

First (most significant) digit of measurement

5

Second digit of measurement

6

Third digit of measurement

7

Fourth (least significant) digit of measurement

8

Mode bits (several can be set at once)

1

Autoranging is enabled

2

Value is negative

9

Mode bits (several can be set at once)

1

DC

2

AC

4

Overload

10

Range, values are the same as with CONF?

11

Unknown (always 0)

12

Temperature unit (probably)

0

not in temperature mode

1

degrees Fahrenheit (not confirmed, need to check)

2

degrees Celsius

13

Mode bits (several can be set at once)

1

Relative mode is enabled

2

Trig Hold-Log mode is enabled

4

Auto Hold-Log mode is enabled

14

Capacitance/AUX mode

0

Capacitance

1

AUX temperature (mV setting in menu is off)

2

AUX mV (mV setting in menu is on)

15

Unknown (always 0)

U124xC models

The valid commands to retrieve log entries are:

LOG:HAND <index>
LOG:TRIG <index>
LOG:AUTO <index>
LOG:EXPO <index>

Log entries are 14 characters long. Here is an example of log entry:

"01000241100100"

Note that the position of the decimal point is not explicitly given, it must be discerned from the active function and exponent.

Byte

Value

Meaning

1-2

Function

0

Millivoltage

1

Voltage (averaging sense if Alternative unit flag and AC mode)

2

Microcurrent (averaging sense if Alternative unit flag and AC mode)

3

Current (averaging sense if Alternative unit flag and AC mode)

4

Resistance (Continuity if Alternative unit flag)

5

Diode

6

Temperature in °C (or °F if Alternative unit flag)

7

Capacitance

8

Frequency

9

Harmonic ratio

10

%Scale of 4-20 mA (or 0-20 mA if Alternative unit flag)

3

First (most significant) digit of measurement

4

Second digit of measurement

5

Third digit of measurement

6

Fourth digit of measurement

7

Fifth (least significant) digit of measurement

8

Mode bits (several can be set at once)

1

Autoranging is enabled

2

Value is negative

9

Mode bits (several can be set at once)

1

DC

2

AC

4

Overload

10

Exponent

11

Mode bits (several can be set at once)

1

Alternate unit flag

2

Thermocouple type (0 = K, 1 = J)

4

Zero temperature compensation

12

Hold mode

1

Trig-Hold mode

3

Auto-Hold mode

4

Relative mode is enabled (can be combined with *-Hold mode)

13

Mode bits (several can be set at once)

1

Average

2

Min

4

Max

14

Data logging option

0

Manual Log (Hand)

1

Interval Log (Auto)

2

Event Log (Trig)

3

Export Log (Hold button)

Default exponent to be applied to the value for the different functions, in addition to the Exponent field.

Exponent

Function

10e-5

Millivoltage

10e-4

Voltage

10e-7

Microcurrent

10e-3

Current

10e-2

Resistance / Continuity

10e-3

Diode

10e-1

Temperature (both °C and °F)

10e-10

Capacitance

10e-2

Frequency

10e-2

Harmonic ratio

10e-2

%Scale of 4-20 mA / 0-20 mA

U125xx models

The valid commands to retrieve log entries are:

LOG? H<index>
LOG? A<index>

Note that <index> must be exactly 3 digits

Log entries are 13 characters long. Here is an example of log entry:

"0522041404000"

Note that the position of the decimal point is not explicitly given, it must be discerned from the active function and exponent.

Default exponent to be applied to the value for the different functions, in addition to the Exponent field.

Exponent

Function

10-7

Millivoltage

10-5

Voltage

10-7

Current

10-3

Resistance / Continuity

10-19

Conductance

10-5

Diode

10-2

Temperature

10-13

Capacitance

10-3

Frequency

10-5

Duty cycle

10-5

Pulse width

10-3

dBm / dBV

10-3

%Scale of 4-20 mA / 0-20 mA

U128xx models

The valid commands to retrieve log entries are:

LOG:HAND <index>
LOG:TRIG <index>
LOG:AUTO <index>
LOG:EXPO <index>

Log entries are 14 characters long. Here is an example of log entry:

"04235201470002"

Note that the position of the decimal point is not explicitly given, it must be discerned from the active function and exponent.

Byte

Value

Meaning

1-2

Function

0

Millivoltage

1

Voltage

2

Microcurrent

3

Current

4

Resistance (Continuity if Alternative unit flag)

5

Diode

6

Temperature in °C (or °F if Alternative unit flag)

7

Capacitance

8

Frequency

9

Duty cycle (positive pulse, or negative if Alternative unit flag)

10

Pulse width (positive pulse, or negative if Alternative unit flag)

11

dBm (or dBV if Alternative unit flag)

12

%Scale of 4-20 mA (or 0-20 mA if Alternative unit flag)

13

Conductance

3

First (most significant) digit of measurement

4

Second digit of measurement

5

Third digit of measurement

6

Fourth digit of measurement

7

Fifth (least significant) digit of measurement

8

Mode bits (several can be set at once)

1

Autoranging is enabled

2

Value is negative

9

Mode bits (several can be set at once)

1

DC

2

AC

4

Overload

10

Exponent

11

Mode bits (several can be set at once)

1

Alternate unit flag

2

Thermocouple type (0 = K, 1 = J)

4

Zero temperature compensation

12

Hold mode

1

Trig-Hold mode

2

Peak-Hold mode

3

Auto-hold mode

4

Relative mode is enabled (can be combined with *-Hold mode)

13

Mode bits (several can be set at once)

1

Average

2

Min

4

Max

14

Data logging option

0

Manual Log (Hand)

1

Event Log (Trig)

2

Interval Log (Auto)

3

Export Log (Hold button)

Default exponent to be applied to the value for the different functions, in addition to the Exponent field.

Exponent

Function

10-6

Millivoltage

10-4

Voltage

10-9

Microcurrent

10-4

Current

10-3

Resistance / Continuity

10-4

Diode

10-1

Temperature °C

10-2

Temperature °F

10-12

Capacitance

10-3

Frequency

10-3

Duty cycle

10-6

Pulse width

10-3

dBm / dBV

10-2

%Scale of 4-20 mA / 0-20 mA

10-11

Conductance

Event Notifiers

String

Meaning

*0 through *7

Rotary switch position has changed. *0 denotes the most counter-clockwise position (excluding the OFF position), then the value is increased by one for each step in the rotary switch's range. On the U127xx models the codes range from *0 through *10.

*B

Battery voltage dropped to "battery empty" level.

*E

Invalid command.

*I

Probes are connected to the wrong sockets for this mode, "Cerr" is shown on display (not supported on U123xx; it is supported on U124xC, U127xx and U128xx).

*L

A button was pressed (not supported on U123xx, U124xC, U127xx and U128xx). This notifier is only sent once after a command, even if the user presses several buttons.